Electric motors are used in numerous applications where it is necessary to brake the rotation of the rotor which rotates within. Whenever a motor is performing work which must be quickly stopped upon a given input, a braking system must be used to prevent the spinning rotor from excessive coasting once the current supply is interrupted and the electric motor is de-energized. This is particularly true when electric motors are used in conjunction with rotary actuators for controlling the position of device coupled to an actuator, for example, valves, mechanical dampers, and the like, as employed in process control systems.
Process control systems frequently employ valves which may be adjusted for controlling the flow of fluids within a conductor system such as a pipeline. Other types of fluid flow control devices, often encountered in process control systems, include dampers which may be actuated for modulating the flow of gases. Process control systems, in which such a rotary actuator may be used, include heating, ventilating, and air conditioning (HVAC) systems which usually employ a plurality of air handling units comprising interconnected duct work which is associated with mechanical dampers. The duct work and dampers cooperate for controlling the flow of outside ambient air into a conditioned space, for controlling the flow of air from the space to the ambient, and for controlling air flow between cool and warm air ducts.
In the above-mentioned rotary actuator systems, a power transmission is typically connected with an electric motor. The motor provides the power to turn the transmission and thus actuate the damper, valve, etc. Often, the valve or damper movement must be carefully controlled so that when power to the electric motor is switched off, the various motor components will quit rotating as soon as possible. This will prevent movement of the valve or damper beyond the desired point. In such situations, it is desirable to provide a braking action to impede further coasting, i.e., rotation of motor components due to momentum. Once the electric motor is de-energized, a brake is activated to stop the rotation.
An electric motor of the type used in conjunction with actuators is disclosed in Rudich, Jr. et al., U.S. Pat. No. 4,482,847. Rudich, Jr. et al. discloses an actuator, the electric motor for driving the actuator, and a braking system for braking further rotation of the internal components of the electric motor once the electric motor is de-energized. The device disclosed in Rudich, Jr. et al. uses a brake member fixed to a rotor and rotatably mounted about a fixed shaft. The brake member could be made from steel and in some prior devices comprised at least two separate parts, a spindle and a brake plate.
When the rotor spindle was made from steel, lubrication was required between the spindle and the shaft. This lubrication, required for both rotary and sliding motion along the shaft, was provided by an oil bath. At times, rapid starting and stopping caused by electronic line noise resulted in an oscillatory sliding motion against the stationary hardened steel shaft causing rapid premature wear due to displacement of the oil lubrication film and the resultant friction. Also, since some prior art brake members used a separate plate assembled to the end of the steel rotor spindle, the two members tended to wobble due to manufacturing distortions.
The present invention addresses the foregoing drawbacks of known brake members used in conjunction with electric motors.